While Iraq's military claimed Wednesday to have driven back militants battling for control of the country, the chairman of the Joint Chiefs of Staff told Congress that the United States has received a request from the Iraqi government to use its air power in the conflict.

Gen. Martin Dempsey, the senior ranking member of the U.S. armed forces, spoke before the Senate Appropriations Committee Wednesday on Capitol Hill in Washington, saying that the United States' "national security interest (is) to counter (ISIS) where we find them."

ISIS is the Islamic State in Iraq and Syria.

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ISIS militants attack major oil refinery

Comprising mostly Sunni Muslims, ISIS is an al Qaeda splinter group that wants to establish a caliphate, or Islamic state, that would stretch from Iraq into northern Syria. The group has had substantial success in Syria battling Syrian President Bashar al-Assad's security forces. Since launching their offensive in Iraq, ISIS claims to have killed at least 1,700 Shiites.

Hundreds of thousands of Iraqis have fled, prompting fears of a brewing humanitarian crisis.

Qassim Atta, a spokesman for Iraqi security forces, on Wednesday night said an investigation had been ordered into 59 high-ranking security officials accused of leaving their posts. The officials could be executed if found guilty, Atta said.

Concerns over an oil refinery in the Iraqi town of Baiji continued, a key consideration because so much of Iraq's economy depends on its oil production. The country produces 3.3 million barrels per day and has the world's fourth-largest proven crude oil reserves, according to OPEC.

Militants attacked the refinery complex, managing to take over some 60% of it, and set fire to five storage containers, according to police officials. Sporadic clashes are ongoing, they said.

Earlier, Atta said in a televised news conference that Iraqi forces had killed 40 ISIS militants in Baiji, 225 kilometers (140 miles) north of Baghdad, the capital.

"The situation in Tal Afar, Samarra, and Baiji is under control," Atta said.

Atta claimed that Iraq's military were "defeating ISIS in the Baiji area" and that "most of the areas" around the northwestern city of Tal Afar were liberated.

Smoke rises from the front line of a clash south of Kirkuk, Iraq, on Saturday, March 14.

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A group of Kurdish Peshmerga troops take a break from fighting ISIS militants south of Kirkuk on March 14.

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Iraqi security forces and allied Shiite militiamen gather in Tikrit on Friday, March 13. Ousting ISIS from Tikrit is important for the United States-led coalition trying to thwart the extremist group's quest to grow its caliphate. ISIS wants to create an Islamic state across Sunni areas of Iraq and Syria.

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A motorcyclist passes destroyed buildings in the Syrian town of Kobani on Thursday, March 12, after it has been freed from ISIS militants.

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Smoke billows after a mortar shell hit an Anbar governorate building in Ramadi, Iraq, on Wednesday, March 11. ISIS has launched a coordinated attack on government-held areas of the western Iraqi city. Ramadi has been the focus of a fierce ISIS assault since Iraqi forces made gains against the group in Tikrit.

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The parents of 19-year-old Mohammed Musallam react at the family's home in the East Jerusalem Jewish settlement of Neve Yaakov on Tuesday, March 10. ISIS released a video purportedly showing a young boy executing Musallam, an Israeli citizen of Palestinian descent who ISIS claimed infiltrated the group in Syria to spy for the Jewish state. Musallam's family told CNN that he had no ties with the Mossad, Israel's spy agency, and had, in fact, been recruited by ISIS.

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Iraqi Shiite fighters cover their ears as a rocket is launched during a clash with ISIS militants in the town of Al-Alam, Iraq, on Monday, March 9.

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Displaced Assyrian women who fled their homes due to ISIS attacks pray at a church on the outskirts of Damascus, Syria, on Sunday, March 1. ISIS militants recently abducted at least 220 Assyrians in Syria.

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Safi al-Kasasbeh, right, receives condolences from tribal leaders at his home village near Karak, Jordan, on Wednesday, February 4. Al-Kasasbeh's son, Jordanian pilot Moath al-Kasasbeh, was burned alive in a video that was recently released by ISIS militants. Jordan is one of a handful of Middle Eastern nations taking part in the U.S.-led military coalition against ISIS.

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A Kurdish marksman looks over a destroyed area of Kobani on Friday, January 30, after the city had been liberated from the ISIS militant group. The Syrian city, also known as Ayn al-Arab, had been under assault by ISIS since mid-September.

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Smoke billows in Kirkuk as Kurdish Peshmerga fighters take position against ISIS militants on January 30.

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Kurdish people celebrate in Suruc, Turkey, near the Turkish-Syrian border, after ISIS militants were expelled from Kobani on Tuesday, January 27.

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Collapsed buildings are seen in Kobani on January 27 after Kurdish forces took control of the town from ISIS.

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Junko Ishido, mother of Japanese journalist Kenji Goto, reacts during a news conference in Tokyo on Friday, January 23. ISIS would later kill Goto and another Japanese hostage, Haruna Yukawa.

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ISIS militants are seen through a rifle's scope during clashes with Peshmerga fighters in Mosul, Iraq, on Wednesday, January 21.

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An elderly Yazidi man arrives in Kirkuk after being released by ISIS on Saturday, January 17. The militant group released about 200 Yazidis who were held captive for five months in Iraq. Almost all of the freed prisoners were in poor health and bore signs of abuse and neglect, Kurdish officials said.

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Smoke billows behind an ISIS sign during an Iraqi military operation to regain control of the town of Sadiyah, about 95 kilometers (60 miles) north of Baghdad, on Tuesday, November 25.

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Fighters from the Free Syrian Army and the Kurdish People's Protection Units join forces to fight ISIS in Kobani on Wednesday, November 19.

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A picture taken from Turkey shows smoke rising after ISIS militants fired mortar shells toward an area controlled by Syrian Kurdish fighters near Kobani on Monday, November 3.

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Iraqi special forces search a house in Jurf al-Sakhar, Iraq, on Thursday, October 30, after retaking the area from ISIS.

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ISIS militants stand near the site of an airstrike near the Turkey-Syria border on Thursday, October 23. The United States and several Arab nations have been bombing ISIS targets in Syria to take out the militant group's ability to command, train and resupply its fighters.

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A U.S. Air Force plane flies above Kobani on Saturday, October 18.

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Heavy smoke rises in Kobani following an airstrike by the U.S.-led coalition on October 18.

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Cundi Minaz, a female Kurdish fighter, is buried in a cemetery in the southeastern Turkish town of Suruc on Tuesday, October 14. Minaz was reportedly killed during clashes with ISIS militants in nearby Kobani.

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Turkish police officers secure a basketball stadium in Suruc on October 14. Some Syrian Kurds were held there after crossing from Syria into Turkey. Tens of thousands of people fled Kobani to escape ISIS.

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Kiymet Ergun, a Syrian Kurd, celebrates in Mursitpinar, Turkey, after an airstrike by the U.S.-led coalition in Kobani on Monday, October 13.

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Alleged ISIS militants stand next to an ISIS flag atop a hill in Kobani on Monday, October 6.

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In this photo released by the U.S. Air Force on Saturday, October 4, a U.S. Navy jet is refueled in Iraqi airspace after conducting an airstrike against ISIS militants.

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A Kurdish Peshmerga soldier who was wounded in a battle with ISIS is wheeled to the Zakho Emergency Hospital in Duhuk, Iraq, on Tuesday, September 30.

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Syrian Kurds wait near a border crossing in Suruc as they wait to return to their homes in Kobani on Sunday, September 28.

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Tomahawk missiles, intended for ISIS targets in Syria, fly above the Persian Gulf after being fired by the USS Philippine Sea in this image released by the U.S. Navy on Tuesday, September 23.

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Turkish Kurds clash with Turkish security forces during a protest near Suruc on Monday, September 22. According to Time magazine, the protests were over Turkey's temporary decision to close the border with Syria.

Kurdish Peshmerga fighters fire at ISIS militant positions from their position on the top of Mount Zardak, east of Mosul, Iraq, on Tuesday, September 9.

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Iraqi volunteer fighters celebrate breaking the Amerli siege on Monday, September 1. ISIS militants had surrounded Amerli, 70 miles north of Baquba, Iraq, since mid-June.

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Kurdish Peshmergas fight to regain control of the town of Celavle, in Iraq's Diyala province, on August 24.

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Peshmerga fighters stand guard at Mosul Dam in northern Iraq on Thursday, August 21. With the help of U.S. military airstrikes, Kurdish and Iraqi forces retook the dam from ISIS militants on August 18. A breach of the dam would have been catastrophic for millions of Iraqis who live downstream from it.

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Displaced Iraqis receive clothes from a charity at a refugee camp near Feeshkhabour, Iraq, on Tuesday, August 19.

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Peshmerga fighters inspect the remains of a car that reportedly belonged to ISIS militants and was targeted by a U.S. airstrike in the village of Baqufa, north of Mosul, on August 18.

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Kurdish Peshmerga fighters fire at ISIS in Khazair, Iraq, on Thursday, August 14.

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Aziza Hamid, a 15-year-old Iraqi girl, cries for her father while she and some other Yazidi people are flown to safety Monday, August 11, after a dramatic rescue operation at Iraq's Mount Sinjar. A CNN crew was on the flight, which took diapers, milk, water and food to the site where as many as 70,000 people were trapped by ISIS. But only a few of them were able to fly back on the helicopter with the Iraqi Air Force and Kurdish Peshmerga fighters.

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Thousands of Yazidis are escorted to safety by Kurdish Peshmerga forces and a People's Protection Unit in Mosul on Saturday, August 9.

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A Baiji oil refinery burns after an alleged ISIS attack in northern Selahaddin, Iraq, on Thursday, July 31.

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A Syrian rebel fighter lies on a stretcher at a makeshift hospital in Douma, Syria, on Wednesday, July 9. He was reportedly injured while fighting ISIS militants.

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New army recruits gather in Najaf, Iraq, on Wednesday, June 18, following a call for Iraqis to take up arms against Islamic militant fighters.

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Kurdish Peshmerga forces, along with Iraqi special forces, deploy their troops and armored vehicles outside of Kirkuk, Iraq, on June 12.

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Children stand next to a burnt vehicle during clashes between Iraqi security forces and ISIS militants in Mosul on Tuesday, June 10.

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Civilians from Mosul escape to a refugee camp near Irbil, Iraq, on June 10.

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EXPAND GALLERY

That apparently included 50 Siemens employees, including eight Germans, who were holed up in a power station in Baiji but have been freed, according to German officials. The employees are safe and well, CNN was told.

According to German diplomats, around 8,000 German nationals are currently in Iraq.

The casualty numbers and the situation on the ground have not been independently confirmed by CNN.

Saudi government denial

Iraqi Prime Minister Nuri al-Maliki struck a defiant note in his weekly address, insisting that Iraqi authorities "will win" despite the setbacks of the past week, during which Iraqi security forces crumbled in Mosul and elsewhere before the militants' advance.

"We absorbed the initial shock of the military operations and now we are on the rebound we will respond and keep the momentum," he said. "What happened was a catastrophe, but not every catastrophe is a defeat."

Al-Maliki blamed political paralysis, not military weakness, for the crisis. He urged Iraqis to unite against terrorism, insisting that the political process would begin to move now that elections are over.

Critics blame al-Maliki and his Shia-dominated government for the worsening sectarian division in Iraq.

Earlier, the Prime Minister's office released a statement accusing Saudi Arabia of appeasing terrorists and providing radical groups with material and moral support.

"The Saudi government must bear responsibility of the serious crimes committed by these groups," the statement read.

On Wednesday in a strongly worded statement, the Saudi Arabian government denied that the kingdom provides "either moral or financial support to ISIS or any terrorist networks. Any suggestion to the contrary is a falsehood."

The Saudis blamed the Iraqi Cabinet for "exclusionary policies (that) have fomented this current crisis."

Obama, congressional leaders huddle

On Tuesday, ISIS militants battled Iraqi security forces for control of Baquba, only 60 kilometers (37 miles) from Baghdad.

The fighters have "made a great advance on Baquba" and are pushing very hard to take it, officials said Tuesday. But the city has not fallen.

Holding on to cities so close to the capital, where nerves are fraying, may prove crucial to al-Maliki's government.

What is happening in Iraq is increasingly taking on the urgency of an international crisis.

On Wednesday, U.S. President Barack Obama huddled with congressional leaders.

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"We had a good discussion. The President basically just briefed us on the situation in Iraq and indicated he didn't feel he had any need for authority from us for the steps that he might take and indicated he would keep us posted," Senate Minority Leader Mitch McConnell told reporters.

Also Wednesday, U.S. Vice President Joe Biden spoke with al-Maliki, and other leaders, by phone.

"He emphasized the need for the Prime Minister -- and all Iraqi leaders -- to govern in an inclusive manner, promote stability and unity among Iraq's population, and address the legitimate needs of Iraq's diverse communities," according to a statement from the White House.

The administration faces some tough choices.

Obama has ruled out ground troops. Airstrikes remain under consideration.

A video message purportedly from a Moroccan Sunni cleric called for attacks against U.S. embassies worldwide if the United States conducts airstrikes in Iraq. The message, believed to be from Sheik Mohammad Ali Algzouli, was posted online Tuesday.

Turkish citizens kidnapped

Iraq's neighbor, Turkey, and India have also seen its citizens caught up directly in the conflict.

A Turkish official told CNN on Wednesday that the country is aware "some construction workers in Kirkuk may have been kidnapped. We are following developments." Kirkuk is one of the provinces that has seen heavy fighting.

The latest reported incident follows the abduction of 48 Turkish citizens last week from the Turkish Consulate in Mosul, Iraq's second-largest city. It fell to ISIS militants just over a week ago after Iraqi forces collapsed.

The Turkish Foreign Ministry said Tuesday that all efforts continue toward the safe return to Turkey of the consulate staff and 31 other Turkish citizens held in Mosul's Geyara district.

India's Ministry of External Affairs said Wednesday that 40 Indian nationals working in Mosul for a construction company had been kidnapped in Iraq.

Their location is unknown, ministry spokesman Syed Akbarruddin told reporters in New Delhi. The kidnapped Indians work for the Tariq Noor Al Huda Co., based in Baghdad, he said.

Families -- mostly Shiite -- are leaving Baquba and other Iraqi cities in droves. They're taking whatever possessions they can carry. Some are even taking livestock.

Over the past week or so, ISIS militants have pressed forward, taking large chunks of territory. They have had several significant victories, including Tal Afar, Mosul and two villages in Diyala province.

In their advance through Iraq, the militants have had support from Sunni tribes and militia angered by al-Maliki and his government, which they accuse of marginalizing Sunni concerns.

The tribes, who fought alongside U.S. forces to push al Qaeda militants out of Iraq in 2006 and 2007, want to see al-Maliki forced from power but their continued backing for ISIS is not guaranteed.

Baghdad offensive

The Obama administration appears to have some confidence that the insurgents will fail to take the capital.

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A senior intelligence official drew a contrast between Iraqi Security Forces defending Baghdad and other Iraqi soldiers who melted away in the face of ISIS fighters across northern Iraq earlier this month.

"ISF elements protecting Baghdad are assessed to be more loyal to the regime and are composed of mostly Shia who are more likely to resist," the official said. "These factors, plus the fact that they are defending the capital, should motivate the ISF elements in Baghdad to put up a better fight."

Al-Maliki fired four top military officers that "deserted and did not fulfill their professional and national duty," according to a statement read Tuesday on state TV.

Among them were the operations command chief for Nineveh province -- of which Mosul is the capital -- and two of his officers, the statement said. Another commander will be tried in a military court in absentia for fleeing the battlefield to an unknown place.

President Hassan Rouhani said Wednesday that Iran would spare no effort to protect holy Shiite shrines in neighboring Iraq from "killers and terrorists," Iran's state-run Islamic Republic News Agency reported.

A senior security official in Baghdad told CNN last week that Iran had sent about 500 Revolutionary Guard troops to help fight the ISIS militants.

Rouhani denied the report over the weekend but said he would be open to helping if asked, though with strategic guidance rather than troops. Iran is often accused of using proxies to hold sway in the region but has never militarily intervened in any sovereign country.

Iran is closely allied with the Shia-led government of Iraq.

The United States and Iran held "very brief discussions" in Vienna, Austria, about Iraq and the threat posed by ISIS on Monday.

Forces on standby

Still, leaving nothing to chance, the Pentagon is moving more firepower and manpower into the region.

Already at the U.S. Embassy in Baghdad, dozens of Marines and Army troops have moved in to beef up security. Another 100 personnel are in the region to provide support if needed, the Pentagon said.

The aircraft carrier George H.W. Bush and five other warships are now in the Persian Gulf. More than 500 Marines and dozens of helicopters are on standby.

Speaking at a CNN town hall meeting on Tuesday, Hillary Clinton, former secretary of state and a potential 2016 presidential candidate, said the Iraqi government made a "mistake" by failing to forge an agreement with the United States to keep American troops in Iraq after the war.

The United States wanted American soldiers to be immune from prosecution. The Iraqi government resisted.

"It's imperative that the government of Iraq, currently led by Maliki, be much more inclusive, much more willing to share power, involve all the different segments of Iraq," she said.

"And I believe strongly that if Maliki is not the kind of leader who can do that, then the Iraqi people need to think seriously about the kind of leader they need to try to unite Iraqis against what is a terrible, imminent threat from these most extreme terrorists."